1. Field of Invention
The present invention relates to a semiconductor light emitting device with a doped wafer-bonded interface and/or a less absorbing etch stop layer.
2. Description of Related Art
Light emitting diodes (LEDs) are widely accepted as light sources in many applications that require low power consumption, small size, and high reliability. Energy-efficient diodes that emit light in the yellow-green to red regions of the visible spectrum contain active layers formed of an AlGaInP alloy. FIGS. 1A-1B and 2A-2B show the fabrication of a conventional transparent substrate (TS) AlGaInP LED. In FIGS. 1A-1B, an etch stop layer 12 such as a 1000 Å n-In0.5Ga0.5P layer, is grown over a semiconductor substrate 10, typically GaAs. Device layers 14, including a lower confining layer, at least one (AlxGa1-x)yIn1-yP active layer, and an upper confining layer, all placed in a double heterostructure configuration, are grown over etch stop layer 12, followed by an optional thick (for example, between 5 and 100 μm thick) window layer 16, often p-type GaP grown by vapor phase epitaxy. The confining layers are made of a transparent semiconductor and enhance the internal quantum efficiency of the LED, defined as the fraction of electron-hole pairs in the active layer that recombine and emit light. The window layer 16, also a transparent semiconductor, increases the spread of electric current across the active layer and enhances the internal quantum efficiency of the diode. The light emitting region may consist of a single thick uniform composition layer or a series of thin wells and barriers.
GaAs is preferred as a growth substrate because it is lattice matched to (AlxGa1-x)yIn1-yP at compositions favored for the formation of LEDs that emit light in the yellow-green to red regions of the visible spectrum, at y˜0.5. Since GaAs is absorbing, it is typically removed and replaced by a transparent substrate 18, as illustrated in FIGS. 2A-2B. GaAs substrate 10, shown in FIGS. 1A-1B, is removed by an etch that etches GaAs at a much faster rate than etch stop layer 12. A transparent substrate 18, typically n-type GaP, is wafer bonded to the lower surface of the epitaxial structure (etch stop layer 12 in FIGS. 2A-2B), generally by annealing the structure at an elevated temperature while uniaxial force is applied. LED chips are then processed from the bonded wafers using conventional metal contacts and chip fabrication techniques suitable for the p-type epitaxial GaP anode and the n-type wafer-bonded GaP cathode.